The present disclosure is related to an optical film which is favorably suited for use as a polarizing plate protecting film, a polarizing plate, a liquid crystal display device, and a method for producing an optical film.
In recent years, liquid crystal display devices are widely employed in liquid display panels for televisions, personal computers, cellular phones and digital cameras. Generally, a liquid crystal display device includes a liquid crystal panel member having a polarizing plate on both sides of liquid crystal cells, and display is performed by controlling light emitted from a backlight member with the liquid crystal panel member. The polarizing plate is configured with a polarizer and at least one polarizing plate protecting film.
The quality of recent liquid crystal displays is improving, and applications thereof are also becoming diversified. Use of liquid crystal displays in various environments is being considered, and therefore there is demand for durability compatible with such environments as well as performance stability. In liquid crystal display devices which are to be employed outdoors, there is demand for durability such as hardness and brittleness sufficient to withstand use outdoors, stable dimensional properties with respect to temperature and humidity changes, and stability of optical properties in polarizing plate protecting films for protecting the surfaces of polarizing plates. In particular, in a high humidity environment, degradation of polarizers due to moisture absorption is a problem, and achieving low moisture permeability in polarizing plate protecting films is an important objective.
Japanese Unexamined Patent Publication No. 2007-297604 discloses an optical film having superior durability in high temperature and high humidity environments, which is produced by curing a thermosetting resin composition containing a polylactic acid resin and an epoxy resin and/or oxetane resin as essential components. In the Examples of Japanese Unexamined Patent Publication No. 2007-297604, the pencil hardness of 80 μm thick films formed on the PET films (polyethylene terephthalate films) is as high as H, and as low as 6B. With respect to the water absorption rates of these Examples, it is described that the lowest water absorption rate is 2.8%.
Japanese Unexamined Patent Publication No. 2013-174861 discloses a polarizing plate having at least one polarizing plate protecting film formed by at least one resin and a polarizer durability improving agent, which is a compound having at least one hydrogen bonding hydrogen-donating group and in which the ratio of the molecular weight/number of aromatic rings is 300 or less.
Japanese Unexamined Patent Publication No. 2013-174861 discloses that according to the polarizing plate of Japanese Unexamined Patent Publication No. 2013-174861, polarizer durability is superior even in an environment of high temperature and high humidity, the curl is small, that warping or distortion of a liquid crystal panel due to environments, and display unevenness caused thereby are unlikely to occur.